ACTG 298 - This is a randomized double-blind, placebo-controlled Phase II trial to measure the virologic and immunological effect of ZDV vs. d4T vs. ZDV in HIV-infected patients greater than 11 years of age with CD4 cell counts between 300-600 and no previous nucleoside experience. The duration of the study will be 48 weeks after the last subject is enrolled with a blinded study extension of 12 weeks while data obtained from the study is being analyzed.